Avoid memory access errors if llength() overflows

llength() is currently a 'short' which can overflow and result in signed
numbers if line lengths are larger than 32k.  We'll fix the overflow
separately, but before we do that, just use a signed int to hold the
value so that we don't overrun memory allocations when we converted that
negative number to a large positive unsigned integer.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>